Internal Audio DAC Card

Optional internal mastering quality DAC card for Crookwood systems.

Overview

The Crookwood DAC card is a high performing, mastering quality DAC card, that can be fitted into most of our products. It is a no frills design that takes AES or SPDIF in only, and provides balanced analogue out. Because all of our products already provide connectors, power supply and logic, the cost of the card is very low, ridiculously low in fact for the quality of conversion it provides.

There are many fine DAC s on the market, but to date our mastering clients have found this little card holds its own against other DAC s, old and new. If you have got one of our consoles or controllers, it’s certainly worth purchasing these DACs to improve the overall quality of your conversion.

Features

Compact DAC card that can be fitted to any of our consoles, controllers or big preamps, either at order time or retrospectively.

AES or SPDIF PCM input from 32KHz to 192KHz.

Will work with any bit rate 16-24 bits.

Can be ganged to work with 5.1, 7.1 or larger formats. All cards naturally sync perfectly together.

Jitter immune design, will sound identical irrespective of the quality of the incoming digital carrier stream – it just works!

S/N and dynamic range of -119.5dB A weighted.

Frequency response, as per incoming sample rate/2.

How we do it

We’ve been designing DAC s since the mid nineties, and this is our 7th incarnation of our DAC. You may not know it, but there are only a handful of semiconductor manufacturers who make decent DAC chips, so nearly all commercial pro audio DAC boxes on the market use chips from these few vendors. What makes the difference in sound then is not really the actual digital to analogue conversion process, but the other, rather boring bits around the DAC chip.

Clock Recovery

The major factor is how well you recover the data clock from the incoming digital data. Poor data clock, poor analogue output. Traditionally this was the role of the Phase Locked Loop ( PLL), a simple, well documented analogue bit of circuitry, but difficult to actually achieve in practice. Until about 2003, this was the limiting factor in DAC performance. However around 2003, several semiconductor factories started to make very good sample rate converter chips. Unlike the analogue PLL s, these were effectively digital signal processors (DSP s) and by isolating the data clock from the precision DAC clock, they could do what a PLL did, but a whole lot better.

The net effect is that our DACs sound the same irrespective of the quality or length of the digital cable, it’s routing, or the quality of the AES driver in the DAW. Suddenly you can hear the music, and it’s consistent. Result.

There has been some criticism in the use of SRCs, in that they are adding an additional digital process to the audio signal. This is true, however it’s also worth pointing out that the DAC chips also DSP the audio. The SRC chip just does it better than the DSP inside the DAC chips, and the combination of a SRC and a locally clocked DAC at a fixed high sample rate is very powerful, certainly better than a regular analogue PLL or VCO system.

Layout

After the clock recovery, the layout of the DAC is the most important factor. You’ve got fragile analogue signals next to stupidly fast digital signals, power lines and clocks. The only way to get it to work well is with good layout.

Our DAC cards are quite a lot larger than most – typically a competitor would get an 8 channel card in the size of our 2 channel card. This is because we like space, and they like profit ( small size things are cheaper to make and ship). All critical bits are kept well away from other parts, and in the world of physics, stuff attenuates in level with distance. It’s this layout that gives us a huge advantage over other DACs.

One interesting nugget is the concept of resolution. Some recent DAC chips are 6dB quieter than ours. It’s natural to think that they therefore will have 6dB more “resolution”, but it doesn’t work like that. They have 6dB less noise, so if you’re summing loads of channels you get an advantage, but for monitoring or recording, what’s more important is what your noise floor sounds like. With a good DAC, you can play and hear a sine wave, say at -20 or -30dB below the noise floor of the DAC. It’s all to do with the DAW dither quality and the layout quality of the DAC. Try it with your DAW and one of our DACs, you can hear the tone in the noise. This is all down to our layout, stopping digital rubbish from entering the audio noise floor.

This is why despite some advances in DAC technology, our 5 yr old DAC design still holds it’s own, and will continue to do so – you can hear the audio in that there noise floor!

Analogue Bits

Most electronic engineers out there are trained in digital technology – it’s sexy, current, fast moving and it’s where the jobs are. Sadly however once you’ve recovered the data, a DAC is an analogue device, which a lot of folk just don’t get. Most commercial DACs use analogue circuitry straight out of the semiconductor manufacturers data sheet. They work fine, but if you know your analogue, they can work better.

Thankfully Crookwood are analogue engineers, who’ve learnt digital, rather than the other way around, so our analogue circuitry is very good, and we pay proper attention to power supplies, clocks, passives and grounding.

The End Result

The end result is a very competent DAC card. Each DAC card is fully self contained, not reliant on wobbly central power supplies or ground systems, or distributed clocks. It has a clean noise floor, excellent accurate conversion, and is very affordable.